Messages in this thread Patch in this message | | | Date | Thu, 26 Mar 2015 11:14:37 +0000 | From | Juri Lelli <> | Subject | Re: [PATCH v13] sched/deadline: support dl task migration during cpu hotplug |
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Hi,
On 25/03/2015 23:47, Wanpeng Li wrote: > I observe that dl task can't be migrated to other cpus during cpu hotplug, > in addition, task may/may not be running again if cpu is added back. The > root cause which I found is that dl task will be throtted and removed from > dl rq after comsuming all budget, which leads to stop task can't pick it up > from dl rq and migrate to other cpus during hotplug. > > The method to reproduce: > schedtool -E -t 50000:100000 -e ./test > Actually test is just a simple for loop. Then observe which cpu the test > task is on. > echo 0 > /sys/devices/system/cpu/cpuN/online > > This patch adds the dl task migration during cpu hotplug by finding a most > suitable later deadline rq after dl timer fire if current rq is offline, > if fail to find a suitable later deadline rq then fallback to any eligible > online cpu in order that the deadline task will come back to us, and the > push/pull mechanism should then move it around properly. > > Suggested-and-acked-by: Juri Lelli <juri.lelli@arm.com> > Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> > --- > v12 -> 13: > * move hotplug stuff to CONFIG_SMP in order to fix the error reported by kbuild test robot > v11 -> v12: > * s/WARN_ON/BUG_ON > v10 -> v11: > * fix codes comments > * tsk_cpus_allowed(p) shouldn't be on separate lines > * introduce a helper function to fold dl task migration during cpu hotplug support > v9 -> v10: > * fix the "WARNING: line over 80 characters" > * handle no admission control > v8 -> v9: > * align tsk_cpus_allowed(p) to cpu_active_mask > * add WARN_ON(1) > * don't resched_curr if later_rq come from the cpumask_any_and() > v7 -> v8: > * remove rd->span related modification since Pang's commit 16b269436b72 > (sched/deadline: Modify cpudl::free_cpus to reflect rd->online) merged > upstream, which Juri pointed out can handle the exclusive cpusets. > * rebase > v6 -> v7: > * rebase > v5 -> v6: > * add double_lock_balance in the fallback path > v4 -> v5: > * remove raw_spin_unlock(&rq->lock) > * cleanup codes, spotted by Peterz > * cleanup patch description > v3 -> v4: > * use tsk_cpus_allowed wrapper > * fix compile error > v2 -> v3: > * don't get_task_struct > * if cannot preempt any rq, fallback to pick any online cpus > * use cpu_active_mask as original later_mask if cpu is offline > v1 -> v2: > * push the task to another cpu in dl_task_timer() if rq is offline. > > kernel/sched/deadline.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 59 insertions(+) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 24c18dc..60b7e90 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -218,6 +218,54 @@ static inline void set_post_schedule(struct rq *rq) > rq->post_schedule = has_pushable_dl_tasks(rq); > } > > +static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq); > + > +static void dl_task_migration(struct rq *rq, struct task_struct *p) > +{ > + struct rq *later_rq = NULL; > + bool fallback = false; > + > + later_rq = find_lock_later_rq(p, rq); > + > + if (!later_rq) { > + int cpu; > + > + /* > + * If we cannot preempt any rq, fall back to pick any > + * online cpu. > + */ > + fallback = true; > + cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p)); > + if (cpu >= nr_cpu_ids) { > + if (dl_bandwidth_enabled()) { > + /* > + * Fail to find any suitable cpu. > + * The task will never come back! > + */ > + BUG_ON(1); > + return; > + } > + /* > + * If admission control is disabled we > + * try a little harder to let the task > + * run. > + */ > + cpu = cpumask_any(cpu_active_mask); > + } > + later_rq = cpu_rq(cpu); > + double_lock_balance(rq, later_rq); > + } > + > + deactivate_task(rq, p, 0); > + set_task_cpu(p, later_rq->cpu); > + activate_task(later_rq, p, ENQUEUE_REPLENISH); > + > + if (!fallback) > + resched_curr(later_rq); > + > + double_unlock_balance(rq, later_rq); > +} > + > #else > > static inline > @@ -536,6 +584,17 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) > sched_clock_tick(); > update_rq_clock(rq); > > +#ifdef CONFIG_SMP > + /* > + * So if we find that the rq the task was on is no longer > + * available, we need to select a new rq. > + */ > + if (unlikely(!rq->online)) { > + dl_task_migration(rq, p); > + goto unlock; > + } > +#endif > + > /* > * If the throttle happened during sched-out; like: > * >
I think we could have better naming and the BUG_ON part could be simplified. I'd propose something like this (sorry, it is based on one of your previous versions.. I'm a bit struggling keeping up with the pace ;)).
Thanks!
--- kernel/sched/deadline.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 1820d1b..2b260a9 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -518,7 +518,7 @@ static int start_dl_timer(struct sched_dl_entity *dl_se, bool boosted) static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq); -static void dl_task_migration(struct rq *rq, struct task_struct *p) +static void dl_task_offline_migration(struct rq *rq, struct task_struct *p) { struct rq *later_rq = NULL; bool fallback = false; @@ -535,14 +535,12 @@ static void dl_task_migration(struct rq *rq, struct task_struct *p) fallback = true; cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p)); if (cpu >= nr_cpu_ids) { - if (dl_bandwidth_enabled()) { - /* - * Fail to find any suitable cpu. - * The task will never come back! - */ - WARN_ON(1); - return; - } + /* + * Fail to find any suitable cpu. + * The task will never come back! + */ + BUG_ON(dl_bandwidth_enabled()); + /* * If admission control is disabled we * try a little harder to let the task @@ -609,11 +607,11 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) update_rq_clock(rq); /* - * So if we find that the rq the task was on is no longer + * If we find that the rq the task was on is no longer * available, we need to select a new rq. */ if (unlikely(!rq->online)) { - dl_task_migration(rq, p); + dl_task_offline_migration(rq, p); goto unlock; } -- 2.3.0
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